Add algorithm for processing constraints for video content capture.

content/renderer/media/media_stream_constraints_util_video_content.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_VIDEO_CONTENT_H_
+#define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_VIDEO_CONTENT_H_
+
+#include <string>
+
+#include "content/common/content_export.h"
+#include "media/capture/video_capture_types.h"
+#include "third_party/webrtc/base/optional.h"
+
+namespace blink {
+class WebMediaConstraints;
+}
+
+namespace content {
+
+class CONTENT_EXPORT VideoContentCaptureSourceSelectionResult {
+ public:
+  // Creates a result without value and with the given |failed_constraint_name|.
+  explicit VideoContentCaptureSourceSelectionResult(
+      const char* failed_constraint_name);

[hta - Chromium, 2017/03/10 08:51:46]

In this case, the ownership of failed_constraint_name is unclear (since it's a
char*, and you store the pointer rather than a copy of the pointed-to string).
The destructor of this class is "default", so it seems it does not attempt to
release the failed_constraint_name pointer, so it doesn't take ownership, and
the caller must ensure that it's a string that will remain accessible. Please
document.

[Guido Urdaneta, 2017/03/14 12:29:06]

Done.

+
+  // Creates a result with the given values. Takes ownership of |device_id|.

[hbos_chromium, 2017/03/09 16:51:10]

Since |device_id| is passed by value it is essentially a local variable, owned
by the function by definition. I think the "takes ownership" comment is
redundant and confusing. Remove?

[hta - Chromium, 2017/03/10 08:51:46]

It should probably be const std::string& since it's copied into a local
std::string.

[Guido Urdaneta, 2017/03/14 12:29:06]

I've seen this wording used for when the values is move. Changed to "moved to an
internal field", which is perhaps clearer.

[Guido Urdaneta, 2017/03/14 12:29:06]

It is actually moved (not copied) to a local std::string.
That's the reason it's passed by value (and that the style guide forbids using
r-value references). Updated comment to indicate that more explicitly.

+  VideoContentCaptureSourceSelectionResult(
+      std::string device_id,
+      const rtc::Optional<bool>& noise_reduction,
+      media::VideoCaptureParams capture_params);
+
+  VideoContentCaptureSourceSelectionResult(
+      const VideoContentCaptureSourceSelectionResult& other);
+  VideoContentCaptureSourceSelectionResult& operator=(
+      const VideoContentCaptureSourceSelectionResult& other);
+  VideoContentCaptureSourceSelectionResult(
+      VideoContentCaptureSourceSelectionResult&& other);
+  VideoContentCaptureSourceSelectionResult& operator=(
+      VideoContentCaptureSourceSelectionResult&& other);
+  ~VideoContentCaptureSourceSelectionResult();
+
+  bool HasValue() const { return failed_constraint_name_ == nullptr; }
+
+  // Accessors.
+  const char* failed_constraint_name() const { return failed_constraint_name_; }
+  const std::string& device_id() const { return device_id_; }
+  const rtc::Optional<bool>& noise_reduction() const {
+    return noise_reduction_;
+  }
+  media::VideoCaptureParams capture_params() const { return capture_params_; }
+
+  // Convenience accessors for fields embedded in the |capture_params_| field.
+  int Height() const;
+  int Width() const;
+  float FrameRate() const;
+  media::ResolutionChangePolicy ResolutionChangePolicy() const;
+
+ private:
+  const char* failed_constraint_name_;
+  std::string device_id_;
+  rtc::Optional<bool> noise_reduction_;
+  media::VideoCaptureParams capture_params_;
+};
+
+VideoContentCaptureSourceSelectionResult CONTENT_EXPORT
+SelectVideoContentCaptureSourceSettings(
+    const blink::WebMediaConstraints& constraints);
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_VIDEO_CONTENT_H_